This invention relates to an ink unit for printing press and method and more particularly, to the novel operation and structure of end seals on the ink fountain associated with a cylindrical transfer roll, i.e., an anilox roll.
The type of apparatus to which the invention is directed is seen in co-owned U.S. Pat. No. 5,125,341. A competitive type of unit is seen in European Patent 0 401 250 B1. The current industry standard for sealing the ends of a doctor blade-equipped closed chamber against an anilox or inking roll is to use a polyolefin foam material. Though this material initially seals very well, over a short period of time ink will eventually leak past the seal and dry on the ends of the anilox roll. This dried or semi-dried ink will rapidly destroy the foam seal or because of lack of doctor blade support over the seal, ink can build up under the doctor blade forcing the seal away from the blade which results in severe leaking and "slinging" of ink onto the press via the anilox roll. This problem has a serious economic impact to a printer due to loss of ink, finished product being ruined and the additional time to clean up the press between job changeovers.
The general environment to which the invention pertains is a fluid fountain unit including a transfer roll and a chamber defined by a holder bearing against the transfer roll. The holder supports doctor and containment blades and end seals all bearing against the transfer roll.
The invention includes applying a first lineal pressure by the end seals against the transfer roll and a second and higher lineal pressure against the doctor and containment blades.
We have found advantageous lineal pressures of the order of about 0.1 pounds per lineal inch (0.0175 Newtons per lineal millimeter) to about 2 pounds per lineal inch (0.35 Newtons per lineal millimeter) for the pressure against the transfer roll and pressures of the order of about 1 pound per lineal inch (0.175 Newtons per lineal millimeter) to about 25 pounds per lineal inch (4.4 Newtons per lineal millimeter) against the blades at a roll seal edge deflection of about 0.010 inches (0.25 mm).
In the illustrated embodiment, this lineal pressure ratio is advantageously developed by equipping each end seal on the inner face or wall thereof (which confronts the chamber) with a recess or hollow section generally aligned with the transfer roll as contrasted to the more solid sections under the blades. This results in local seal stiffness greater at the blade bearing surface than at the roll bearing surface. This provides rigid support for the doctor blade to allow good doctoring but to press lightly against the anilox roll for good sealing and seal life. The seal is able to both seal very well initially and also be more wear-resistant to the dried ink on the ends of the anilox roll than a typical foam seal. In tests, the inventive seal lasts about 15 times longer than the foam seal. Equally important, when the inventive seal is worn out, it leaks gradually as against the severe leaking of a foam seal, i.e., there is no catastrophic ink blowout. The value to a printer is minimal ink loss and slinging and less time to clean up between job changeovers.
Other objects and advantages of the invention may be seen in the details of the ensuing specification.